In a large skillet, cook bacon over medium heat until crisp. Drain bacon on paper towels, reserving drippings in the skillet. Crumble bacon; set aside. Reduce heat to medium-low.
Add onion to reserved drippings. Cook for 15 to 20 minutes or until onion is very tender and golden brown, stirring occasionally.
Meanwhile, preheat broiler. Brush baguette slices on both sides with olive oil. Arrange in a single layer on a large baking sheet. Broil 3 to 4 inches from heat for 4 minutes, turning once, until lightly toasted.
Divide onion mixture evenly among baguette slices; sprinkle with blue cheese and bacon. Broil 2 to 3 minutes or until cheese begins to melt. Sprinkle with thyme. Serve warm. Makes 24 appetizers.